Abstract 88: Ephrin receptor A4 is a regulator of metastatic colonization in triple negative breast cancer

Abstract Triple negative breast cancer (TNBC) is the most aggressive breast cancer subtype, affecting more than 40, 000 people in the US. Most TNBC patient deaths are due to distal metastasis, a stage for which effective treatment is not yet available. Metastasis is an inefficient, multi-step process. The bottleneck for establishing the life-threatening macro-metastasis is considered to be metastatic colonization, the step at which cancer cells exit the circulation, survive in the new microenvironment and re-initiate aggressive growth. Numerous studies have found that cancer cell adhesion and migration pathways are required for metastatic colonization. However, the mechanisms by which these pathways are modulated are incompletely understood. Ephrin and Ephrin receptors are a family of proteins with conserved functions related to modulation of cell repulsion and adhesion, particularly in the regulation of pattern formation during development. Here we show that Ephrin Receptor A4, a cell surface receptor tyrosine kinase, regulates cell-cell interactions, migration and metastatic formation in TNBC, similar to its role in development. Depletion of EPHA4 in either human xenograft MDA-MB-231 or mouse syngeneic 4T1 TNBC tumors does not significantly alter tumor growth, but results in differential expression of genes involved in cell-cell adhesion, cell-matrix adhesion, and cell migration. In vitro assays suggest that EphA4 loss promotes collective rather than single cell migration, which can lead to increased metastatic formation. Metastatic lung colonization assays in mice indicate that loss of EphA4 increases metastatic lesions and/or metastatic burden in the MDA-MB-231 and 4T1 tumor models. Consistent with these findings, Ephrin Receptor A4 expression in TNBC is downregulated at metastatic sites relevant to the primary tumor. These results suggest that EphA4 regulates cell adhesion in cancer cells to reduce the efficacy of metastatic colonization. Citation Format: Wenchao Liu, Hoi Wan Lee, Madeline H. Bungert, Geetha P. Yerradoddi, Marsha R. Rosner. Ephrin receptor A4 is a regulator of metastatic colonization in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 88.